Jet grouting has been in commercial use since approximately 1975. In general terms, the technology may be used to efficiently remove underground soils with a high-pressure jet erosion process and replace the removed soil with a stabilization material (i.e., grout). In this way, ailing structures, such as buildings or dams with sagging foundations, may be remediated.
For the jet grouting process to proceed successfully, there generally is a requirement that there be a continuous flush of cuttings (i.e., removed soil) from the point of mixing at the bottom of the drill hole where the jet grouting process is performed. The cuttings need to be removed upward and away from the jet grouting process, typically to the surface. However, if the flow of cuttings to the surface is disrupted along any point of the flow path, the ultra-high injection pressures (3,000 psi-15,000 psi) of the jet grouting process may cause the borehole pressure between the blockage and point of injection to rise to a level that exceeds the fracturing pressure of the soil and, thus, cause a fracture therein. If a soil fraction occurs, the injected stabilization material typically flows away from the borehole and out into the surrounding formation, which prevents the stabilization material from performing its intended purpose. More significantly, though, a soil fracture may cause a mass movement of soil underground, which in turn can lead to severe damage to the foundation of the structure that the jet grouting was intended to repair.
The vagaries of the jet grouting process make is difficult to predict by observation or computer modeling when the fracture pressure of soils may be exceeded. For example, at times the cuttings from the jet grouting process may flow into underground pockets (and not to the surface) such that, while it may appear to an observer at the surface that the flow of cuttings has been interrupted, the process is proceeding with no harmful buildup of pressure. At other times, though, the fracturing pressure of the soil may be exceeded even while there is a flow of the cuttings to the surface because, as it has been found in practice, borehole pressure also is related to the density and rhealogy (viscosity) of the soil cuttings generated during the jet grouting.
As such there is long-felt need for a method or system that may provide a warning to the operators at the surface as to when there is a high risk of soil fracturing during jet grouting due to build up of pressure either in the borehole or along the injection rod. Such a method or system may allow corrective action to be taken so that the jet grouting process can proceed successfully and damage to structures can be prevented. Other objects, features and advantages of the invention will be found throughout the following description, drawings and claims.